Add new mmap(2) flags to permit applications to request specific virtual

address alignment of mappings.
- MAP_ALIGNED(n) requests a mapping aligned on a boundary of (1 << n).
  Requests for n >= number of bits in a pointer or less than the size of
  a page fail with EINVAL.  This matches the API provided by NetBSD.
- MAP_ALIGNED_SUPER is a special case of MAP_ALIGNED.  It can be used
  to optimize the chances of using large pages.  By default it will align
  the mapping on a large page boundary (the system is free to choose any
  large page size to align to that seems best for the mapping request).
  However, if the object being mapped is already using large pages, then
  it will align the virtual mapping to match the existing large pages in
  the object instead.
- Internally, VMFS_ALIGNED_SPACE is now renamed to VMFS_SUPER_SPACE, and
  VMFS_ALIGNED_SPACE(n) is repurposed for specifying a specific alignment.
  MAP_ALIGNED(n) maps to using VMFS_ALIGNED_SPACE(n), while
  MAP_ALIGNED_SUPER maps to VMFS_SUPER_SPACE.
- mmap() of a device object now uses VMFS_OPTIMAL_SPACE rather than
  explicitly using VMFS_SUPER_SPACE.  All device objects are forced to
  use a specific color on creation, so VMFS_OPTIMAL_SPACE is effectively
  equivalent.

Reviewed by:	alc
MFC after:	1 month

1 files changed, 11 insertions, 0 deletions

diff --git a/sys/sys/mman.h b/sys/sys/mman.h
index a178d7c..c5e47a0 100644
--- a/sys/sys/mman.h
+++ b/sys/sys/mman.h
@@ -91,6 +91,17 @@
  */
 #define	MAP_NOCORE	 0x00020000 /* dont include these pages in a coredump */
 #define	MAP_PREFAULT_READ 0x00040000 /* prefault mapping for reading */
+
+/*
+ * Request specific alignment (n == log2 of the desired alignment).
+ *
+ * MAP_ALIGNED_SUPER requests optimal superpage alignment, but does
+ * not enforce a specific alignment.
+ */
+#define	MAP_ALIGNED(n)	 ((n) << MAP_ALIGNMENT_SHIFT)
+#define	MAP_ALIGNMENT_SHIFT	24
+#define	MAP_ALIGNMENT_MASK	MAP_ALIGNED(0xff)
+#define	MAP_ALIGNED_SUPER	MAP_ALIGNED(1) /* align on a superpage */
 #endif /* __BSD_VISIBLE */
 
 #if __POSIX_VISIBLE >= 199309